It's a well-known problem being out there for more than THREE YEARS now. The reference source code published for .net 4.0 had exactly the same problem.
The cause of the problem was once mentioned here:
And the bug in RSCC.ZipHelper.exe is detailed here (post from Zodarion on 28 Oct 2012):
fileStream = new FileStream(handle, FileAccess.Write);
fileStream.Write(buffer, 0, buffer.Length);
fileStream.Write(buffer, 0, count);
SO PLEASE FIX IT FINALLY !!!